1. Field of the Invention
The present invention relates to a single plate type solid-state image pickup device equipped with primary-color type color filters.
2. Description of the Related Art
In a single plate type color solid-state image pickup device, an on-chip color filter, which is designed so that various color filters of plural colors are repetitively disposed in a predetermined arrangement, is formed on a sensor portion to output signals of desired colors.
This on-chip color filter has many kinds of color coding (color arrangements). One of these kinds of color coding has a color arrangement of primary colors (Red, Green, Blue), and it is called as a Bayer arrangement.
The Bayer arrangement is shown in FIG. 11.
If the Bayer arrangement is applied to each four-pixel arrangement (pixel unit) of 2 pixels in the longitudinal direction×2 pixels in the lateral direction, green (G) pixels are obliquely arranged at two places in the diagonal direction, and a red (R) pixel is disposed at one of the other two places while a blue (B) pixel is disposed at the remaining place. As a whole, the arrangement of the pixels is set so that the green pixels are arranged in the oblique direction.
The feature of the Bayer arrangement resides in that when the pixel arrangement is viewed from only the horizontal direction or vertical direction, the green (G) pixels contributing to the resolution exist every pixel. In FIG. 11, Px represents the pixel pitch in the horizontal direction, and Py represents the pixel pitch in the vertical direction.
Accordingly, the Bayer arrangement has the following characteristics.    (1) The spatial frequency characteristic in the horizontal and vertical directions is isotropic.
FIGS. 12A to 12C are spatial frequency characteristics in the horizontal and vertical directions of the three primary colors in the Bayer arrangement of FIG. 11. Specifically, FIG. 12A shows the spatial frequency characteristic for the green G, FIG. 12B shows the spatial frequency characteristic for the red R and FIG. 12C shows the spatial frequency characteristic for the blue B.
From FIGS. 12B and FIG. 12C, each of the red R and the blue B exists every other pixel when the pixels are viewed in each of the horizontal and vertical directions. Accordingly, the horizontal spatial frequency (1/Px) and the vertical spatial frequency (1/Py) are equal to ¼.
On the other hand, from FIG. 12A, the green G exists every pixel when the pixels are viewed in each of the horizontal and vertical directions as described above, and thus the horizontal spatial frequency (1/Px) and the vertical spatial frequency (1/Py) are equal to ½, which is twice as large as these of the red R and the blue B. However, the green G exists every other pixel in the oblique direction, so that the horizontal spatial frequency and the vertical spatial frequency of the green G are equal to those of the red R and the blue B.
Therefore, for the three colors (R, G, B), the horizontal spatial frequency and the vertical spatial frequency are isotropic.    (2) Aperture control signals (outline correcting signals) that provide a comparatively high sense of resolution can be generated by only the green G pixels.
By generating aperture control signals from only the green G pixels, the system can be implemented by using a relatively smaller hardware as compared with a system of generating aperture control signals by using pixels of all three colors.
However, in the color filter having the RGB (primary color type) Bayer arrangement, aperture control signals are generated by using only the signals from the green G pixels, so that the sense of resolution is unbalanced among the colors. When aperture control signals are generated by using only the signals from the green G pixels, the green components dominantly contribute to the spectral characteristic, so that it is difficult to generate aperture control signals from a subject having hue of primary colors (red R, blue B, etc.) containing no green B. That is, for a subject such as a red rose, the outline emphasis is hardly applied to the subject although the subject has high saturation.